The ultimate goal of the project are to improve drug therapy and decrease the toxicity of drugs, economic poisons and other xenobiotics through a better understanding of the mechanisms governing their biotransformation and disposition. Almost all xenobiotics are biotransformed. This almost always terminates their action and facilitates their excretion, but some compounds -- particularly carcinogens -- are activated via biotransformation. Biotransformation therefore figures prominantly among the factors that determine the usefulness or toxicity of drugs and other foreign compounds. Biotransformation of xenobiotics is largely dependent upon hepatic microsomal cytochrome P-450-dependent systems. Our research is concerned with the characterization of these systems in the liver and other organs, with developmental aspects of these systems in the fetus and neonate, with the interaction of these systems with other microsomal systems, and with environmental factors which may influence the amounts and kinds of these systems in various organs. We believe that a better understanding of the microsomal cytochrome P-450 systems will lead to a better understanding of the biotransformation of xenobiotics and that this will contribute substantially to the realization of our ultimate goals -- the improvement of drug therapy and the mitigation of the toxicity of drugs and other xenobiotics.